This research proposal will address the fundamental issue of how visual attention contributes to the construction of enduring representations of objects allowing humans and other primates to make use of information that is no longer available. To investigate this general issue, the recently introduced object-substitution masking paradigm will be studied. Two general questions will be asked: (1) Does the activity of single neurons suggest that behaviorally relevant items are selected by attention even though they are not processed to the point of accurately guiding behavior? (2) Can the substitution of a target by a subsequent mask be observed in the moment-to-moment modulation of neural activity? Object-substitution masking has been shown to be directly related to how attention is deployed in the visual environment because it is only observed when there is strong competition between items in the visual field, such as in visual search task, and can be reduced or eliminated by precuing attention to the target location. Thus, the experiments in this project will require monkeys to search for a target shape among similar distractor shapes. On a proportion of trials the target and several distractors will be presented surrounded by four dots that should effectively mask the items when they remain visible after the objects themselves disappear. An increased understanding of interactions between attention and this new form of masking may ultimately help us understand disorders of normal cognitive processing such as in attention deficit disorder.